Investment and Mortgage-backed Securities - Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of investment securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Available for sale:
Amortized cost	$ 148,863	$ 165,018
Gross unrealized holding gains	425	741
Gross unrealized holding losses	8,586	11,817
Estimated fair value	140,702	153,942
U.S. Government agency securities
Available for sale:
Amortized cost	145,071	160,063
Gross unrealized holding gains
Gross unrealized holding losses	8,520	11,714
Estimated fair value	136,551	148,349
Municipal obligations
Available for sale:
Amortized cost	3,034	3,035
Gross unrealized holding gains	108	83
Gross unrealized holding losses	66	103
Estimated fair value	3,076	3,015
Corporate securities
Available for sale:
Amortized cost	758	1,920
Gross unrealized holding gains	317	658
Gross unrealized holding losses
Estimated fair value	$ 1,075	$ 2,578